Large-caliber small-torque ball valve

The invention discloses a large-caliber small-torque ball valve. An external control assembly is arranged outside connecting bodies on both ends respectively, and the external control assembly is formed as follows: an inlet of a three-way valve is communicated with the connecting bodies, and two outlets are respectively communicated with an internal seal assembly and the external part of a valve body; and the internal seal assembly is formed as follows: an internal ring slot and an external ring slot are arranged at the internal ends of the connecting bodies, a valve seat is installed in the internal ring slot and the external ring slot in an axially sliding manner, and a plurality of springs for compressing the valve seat on the ball body are annularly distributed on the bottom of the internal ring slot. By operating the external control assembly, the internal seal assembly can be controlled to axially move forward and backward, the contact and disengagement between a seal ring of the valve seat and the ball